Viruses belonging to the human herpesvirus family induce a receptor for the Fc portion of IgG during their lytic cycle. We are studying the receptors induced by herpes simplex virus in mammalian cells. We are also studying the induction of Fc receptors in lymphoblastoid cell lines by Epstein-Barr virus. Definition and characterization of the receptor will allow us to gain insights on the possible biological role of the receptor during lytic infection. We are also studying biological properties of human tumors carried in nude mice and of tissue culture cell lines derived thereof. The synthesis of specific tumor products that serve as markers and their regulation is being studied.